1. Field of the Invention
This invention relates to a phenolic resin composition useful for preparing a glass fiber insulation of improved moisture resistance. The present invention particularly relates to a resole-type phenolic resin containing a borate salt which is useful for preparing a dark colored insulation binder for glass fibers and to the glass fiber insulation containing the cured resin.
2. Description of Related Art
Phenolic resins have long been employed as binders for use with glass fibers in the preparation of insulation products. Historically, such resins have been prepared by reacting a molar excess of formaldehyde with phenol in the presence of a basic catalyst, such as sodium hydroxide. Such alkaline adducts are referred to in the art as phenolic resole resins. When preparing a binder for glass fiber insulation, such resole resins typically are neutralized after their preparation and then mixed with an acidic curative, such as ammonium sulfate, a formaldehyde scavenger, such as ammonia, a silane coupling agent, other diluents such as urea and lignin, and if necessary additional water.
Glass fibers are coated with the aqueous binder solution, usually by spraying, and passed through an oven where they are compressed to the desired thickness and density, and then permanently fixed by heat setting or curing the resin binder. Acid cure has been favored in the art because it produces a glass fiber insulation having good strength characteristics.
More recently, a need has developed in the glass fiber insulation art for binders that produce a dark color when cured. Acid cured phenolic resole resins are relatively light-colored, so carbon black generally has been added to the binder formulation to achieve the necessary coloration. Using carbon black as an additive, however, creates significant handling problems, and thus makes this approach less than desirable.
Alkaline-cured resole resins, unlike their acid-cured counterparts, develop a very dark color through an oxidation reaction upon curing. Alkaline-cured phenolic resole resins also do not emit the strong amine odor associated with resole resins cured with an acid curative such as ammonium sulfate. Unfortunately, alkaline cured phenolic resole resins are rather brittle and thus do not yield binder strengths on a par with acid-cured resins. Glass fiber insulation prepared by curing a phenolic resole resin under alkaline conditions has a low moisture resistance and loses considerable strength when manufactured and/or stored under conditions of high humidity.
The present invention is based on the discovery that the addition of a proper amount of a water-soluble borate salt to a phenolic resole resin having the proper alkalinity significantly improves its moisture resistance after alkaline cure. Thus, the present invention allows the production of a dark colored glass fiber insulation without the need for carbon black and without sacrificing binding strength.